It added that prepayment meter customers should "not be unfairly penalised".
Lindsey Kearton, energy expert at Consumer Focus Wales, said the new rules are "a positive step in the right direction for a fairer energy market".
She added: "Suppliers pricing must be made more competitive for all so the benefits of a free market can spread beyond Direct Debit dual fuel consumers to include in-area, electricity only, standard credit, prepayment and rural consumers."
Consumer Focus recently called for Ofgem to confirm a date for its scheduled review of the wholesale energy market.
It also called for an independent analysis of the current industry efficiency of administration and metering costs.
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